implemented the "ps" command

(1)Added some Standard C functions (also created util.c and stdio.c)
(2)Enabled TRACE_FACILITY for using vTaskList()
(3)Modified the Makefile to compile new C files
(4)Implemented the function for command "ps"
Reference:fboris
added structure instr_data for storing command and its handler
avoid the hardcode by using better way to do text completion